difference between fat eq and channel eq

They sound different. If I recall, the fat eq is less lean on the cpu also. Some people really like the sound of it and say it's . . . well . . . fat (or insert various adjectives derived from the names of famous vintage eq's like "Pultec-ish" etc.)

I do hear a difference but I don't know if that's just because of how you dial in the settings in each plug. Like with the right choices you could make either plug sound like the other.

I personally find the smallish GUI of the fat eq a little annoying to work with and tend to avoid it often. It is certainly an older Logic plug that was included for legacy/compatibility reasons and I think it was the only go-to eq in Logic Audio 6 before they had the channel eq.

Channel EQ has more filters available... 8 vs. 5. (or 4 vs. 3 if you only count the parametric bell filters)

The analyzer feature of channel eq is a great tool as well.

The other big difference that I have noticed is that the Q value in the channel eq can go up to 100 (opposed to 10 in the fat) which makes for a great notch filter...

I'm sure there are other differences, but these three stick out to me

Would be interesting to do a test trying to set identical parameters on the two of them and see if they cancel out.

sometimes are clearer and easier than in the manual. thanks

A general drawback in the Instruments and Effects manual is it doesn't really point out which are "legacy" plug-ins you'd probably only use for their distinctive color, and which are the preferred/replacement current ones. This is also so in the main manual description of the Pitch and Time Machine algorithms.

Of course, the app itself could shift a lot of plug-ins into "Legacy" categories as well -- but maybe it looks like you're "getting more" this way.

The most notable differences between the channel and fat eq's is their operation. The max (tightest) Q that the fat eq can achieve is 10, where the channel eq can go much tighter. So for surgical type eq'ing, the channel eq is a better choice. But that increase in flexibility comes with a price. See below. Obviously the channel eq has more features, like the ability to change the gain-Q coupling characteristics, but one of the things I really like about the fat eq is that you can have two high shelves and two low shelves. Something you cannot do with the channel eq.

One of the ways to look at the computational integrity of a filter is to look at the noise floor when signal is present in the filter. The graph shows both filters (which I matched exactly to null) and shows the channel eq is significantly noisier due to quantization error, etc. The test signals are sine waves at 500 and 750Hz with the resulting level about -1dBFS. Filters are set for hi-pass at 51Hz with a 36dB/octave slope.

The performance of the fat eq is a lot like high end 3rd party eq's like the Sony Oxford. If I had to choose between these 2 for a mastering channel, I'd pick the fat eq hands down.